Instructions for Drytek2 Poly Etch Process Qualification

Purpose: to provide verification and trend of the poly program including etch rates of poly and photoresist, selectivity of those materials, and wafer-to-wafer and within-a-wafer uniformity of etch.

Frequency of the test: to be completed after major maintenance such as cleaning or gas line replacement or on a set schedule to be determined or as needed based on user feedback.

Documentation of results: to be posted on the log sheet located in the assigned book at the tool, posted in the equipment archive for drytek2 on the SNF website and in a file or webpage available to users in data or chart format.

Procedure;

1. Use two wafers with at least 0.5um poly on 1000A oxide, no pattern. Patterned wafers may be used to measure photoresist etch rates, too.
2. Season the chamber for 10 minutes using the poly etch program. Be sure to check the program parameters while seasoning.
3. Measure poly and photoresist thickness using one of the Nanospecs. Be sure to use reference wafer before testing to calibrate the tool. Take readings for the Center, Top, Flat, Right and Left positions of the wafer. Use the statistics option to get averages. Readings should be taken about 15mm from the edge. See Fig. 2. Record results on the Process Qualification Log Sheet.
4. Place the wafers on the top and second electrodes. See Fig. 1.
5. Etch for 2 minutes. Monitor gas flows, RF power and reverse power.
6. Measure poly and photoresist thickness using the same Nanospec. Be sure to use reference wafer before testing to calibrate the tool. Take readings for the Center, Top, Flat, Right and Left positions of the wafer. Readings should be taken in roughly the same place as the first measurements.
7. Record results on the Monitor Log. Record results in data file to get wafer-to-wafer and within-a-wafer
• Subtract the second average reading from the first average reading for poly and for photoresist to get total material etched
• To get the etch rate per minute divide the average total material etched measurements by 2.
• To get the selectivity for poly vs photoresist divide the poly etch rate by the photoresist etch rate

Figure 1: Electrodes with wafers.

Figure 2: Reading placement. Note that the major flat is “down”.